Pathogenesis of fowlpox in laying hens.

Egg production dropped after hens were inoculated with fowlpox virus originally isolated from a natural mild infection. The drop started from the 2nd week and continued to the 5th week after inoculation. All birds developed focal lesions at the site of inoculation, and some developed secondary lesions. The drop in individual birds was related to the severity of lesions. Birds challenged with fowlpox virus fifteen months after vaccination with pigeon pox vaccine were susceptible.